1. Field of the Invention
This invention generally relates to a bimetallic indicator, in particular to a bimetallic indicator for use in a heat gauge indicating a temperature of an engine cooling water of an automobile or a pressure gauge indicating a pressure of a pressurized air supplied to a turbo engine, and so forth.
2. Description of the Prior Art
A conventional bimetallic indicator of this type is for example illustrated in FIG. 1. In the drawing, the indicator is a heat gauge used in an automobile, which comprises a thermistor sensor 1 in which resistance value is varied in accordance with temperature change in a cooling water of an automobile engine or the like and a bimetal 3 on which a heating coil 2 is wound. In proportion to change of the resistance value in the thermistor sensor 1, electric current corresponding to the change is supplied to the heating coil 2, thereby the bimetal 3 being heated and then deformed. A movable pin 3a mounted to the bimetal 3 is slidably inserted into a slit 5a formed on an end portion of a pointer 5 which is rotationally supported by a pointer axis 4. Accordingly, when an amount of electrical current in proportion to the temperature change of the cooling water is supplied to the heating coil 2, the heating coil 2 is heated and the bimetal 3 is deformed by the heat. As a result, the movable pin 3a is moved by the deformation of the bimetal 3 and then the pointer 5 is also rotated with respect to the pointer axis 4 in accordance with the movement of the movable pin 3a, thereby the temperature of the cooling water being indicated on scales of a scale plate 6 by the pointer 5.
In the type of the indicator, however, generally, there are dispersions in indication of the indicator and resistance value of the thermistor sensor, as well as there may be a difference in a temperature of a cooling water according to the type of an engine of an automobile. Due to these factors, when the indicator is equipped in an automobile, large dispersion in indication of the indicator is apt to be caused.
In this case, for example, if such a dispersion is caused in a high temperature range over the actual temperature which is in a normal condition of the cooling water of the engine, the driver may be anxious about a possibility of over-heat. On the other hand, in a case where such a dispersion is caused in a low temperature range under the actual temperature, the driver may be anxious about that something is wrong with the automobile due to the temperature of the cooling water being not rose.
In view of the foregoing disadvantages of the conventional indicator, the improved indicator as shown in FIG. 2 was proposed, which is described in the Publication of the Japanese Utility Model Application No. 59-115326. In the improved- indicator, a movable plate 7 with a pointer 5 is fixed to the pointer axis 4. The movable plate 7 has a meander guide slit 7a. In the middle portion of the guide slit 7a, there is provided a pointer non-moved portion 7'. Said portion 7' is formed along the line that the movable pin 3a attached to the bimetal (not shown) is moved when a temperature of the cooling water is in a normal condition. As a result, in a case where the movable pin 3a displaces in the portion 7' the pointer 5 is not moved. Therefore, even if the dispersion of the indication is caused when the temperature is in the normal condition, the pointer keeps on indicating a fixed value in an indicating zone indicating that the temperature resides in the normal condition, thereby it can be prevented that the driver becomes anxious about due to reading the uncorrect indication of the pointer caused by the dispersion.
In the improved bimetallic indicator, however, there is the other disadvantage that an angle which the pointer 5 can be moved on a scale becomes small. This is because the movable plate 7 and the pointer 5 that cooperates with the movable plate 7 are being stopped during the guide pin 3a runs within the portion 7', in which the movable plate 7 and the pointer 5 can not be moved in spite of the deformation of the bimetal 3. In addition, there is further disadvantage that swinging of the pointer due to external force such as vibration during the movable pin 3a is positioned in the portion 7a' is apt to be caused. This is because a clearance between the movable pin 3a and slit 7a' is large in the rotational direction of the-pointer 5, so that the pointer 5 is liable to be affected by the external force.